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Abstract

Titanium phosphate is currently a promising material for proton exchange membrane fuel cells applications (PEMFC) allowing for operation at high temperature conditions. In this work, titanium phosphate was synthesized from tetra iso-propoxide (TTIP) and orthophosphoric acid (H<sub>3</sub>PO<sub>4</sub>) in different ratios by a sol gel method. High BET surface areas of 271 m<sup>2</sup>.g<sup>-1</sup> were obtained for equimolar Ti:P samples whilst reduced surface areas were observed by varying the molar ratio either way. Highest proton conductivity of 5.4×10<sup>-2</sup>S.cm<sup>-1</sup> was measured at 20°C and 93% relative humidity (RH). However, no correlation was observed between surface area and proton conductivity. High proton conductivity was directly attributed to hydrogen bonding in P-OH groups and the water molecules retained in the sample structure. The proton conductivity increased with relative humidity, indicating that the Grotthuss mechanism governed proton transport. Further, sample Ti/P with 1:9 molar ratio showed proton conductivity in the order of 10<sup>-1</sup> S.cm<sup>-1</sup> (5% RH) and ~1.6×10<sup>-2</sup>S.cm<sup>-1</sup> (anhydrous condition) at 200°C. These proton conductivities were mainly attributed to excess acid locked into the functionalised TiP structure, thus forming ionisable protons.